Size, Charge and Dose Dependent In-vitro Kinetics of Polystyrene Nanoparticles

The aim of the study described herein is to quantify the in-vitro kinetics of internalization of polystyrene nanoparticles (PS NPs) by cells. We used different charges, sizes and doses of fluorescently labelled PS NPs. Nanoparticles were characterized with UV-Vis, Fluorescence emission Dynamic Light Scattering (DLS) and Zeta potential for knowing their absorption, fluorescence spectra, size, charge, respectively. Additionally, cell viability was tested to know the toxicity of PS NPs. The quantitative uptake, the kinetics profile and rate of uptake were studied by using a new in-vitro fluorescence assay. This was achieved quantitatively and qualitatively by fluorescent plate reader and confocal imaging, respectively. It was found that the amine PS NPs are higher in cytotoxicity than the carboxy PS NPs due to the proton sponge phenomenon. It was observed that the fraction uptake of PS NPs changes by changing the physiochemical properties as charge, size & dose. The fraction uptake of neutral and amine PS NPs was higher than that of carboxy PS NPs. For the neutral PS NPs, the uptake depends on the macropinocytosis. For the amine PS NPs, the uptake depends on the electrostatic interaction and the rapid regeneration of new binding sites. Regarding the dose of PS NPs, for the amine PS NPs, it was found that the concentrations lower and higher than 5nM had lower fraction uptake, because the 5nM achieved the balance between the available number of binding sites and the rapid regeneration of new binding sites. For the kinetics profile of the amine and carboxy PS NPs, by comparing both of them, it was observed that the rate of uptake of applied doses lower than 5nM was different, but higher than 5nM was similar. However, for the neutral Ps NPs, they exhibit a steady state of rate of uptake in between the amine and carboxy PS NPs. Also, it was confirmed by the confocal images that as the concentration of amine PS NPs increase, the stress on the cells increase, leading to the cell death. These results were aligned with the results obtained from the cytotoxicity test